JPH0652815B2 - Laser equipment - Google Patents

Description

The present invention relates to improving the quality of a laser beam generated from a laser device.

[Conventional technology]

FIG. 17 shows, for example, a laser handbook (Ohm,
FIG. 1 is a cross-sectional configuration diagram showing a conventional solid-state laser device shown in (1982). In the figure, (1) is a solid-state element, for example, if a YAG laser is taken, a rod-shaped crystal made of Y _3-X NdXAl5O ₁₂ , (3) arc lamp, (4) arc lamp
Power source for lighting (3), (5) Condensing reflection mirror,
(6) is, for example, an exit mirror made of glass, (7) is a partially reflecting film made of, for example, TiO ₂ on the inner surface of the exit mirror (6), (8) is on the outer surface of the exit mirror and both side surfaces of the solid-state device. A non-reflective film made of SiO ₂ , for example,
(9) is the laser beam inside the laser resonator, (10) is the laser beam extracted outside, (12) is the outer frame, and (20) is the total reflection mirror.

Next, the operation will be described. The solid-state element (1) is excited by direct light from the arc lamp (3) turned on by the power supply (4) and reflected light from the condensing reflection mirror (5) to form a laser medium. On the other hand, an exit mirror (6) and a total reflection mirror with partial reflectance due to the partial reflection film (7) on the inner surface.
The laser beam (9) that is confined in the so-called stable resonator consisting of (20) is amplified by this laser medium every time it reciprocates between both mirrors, and when it reaches a certain size or more, part of it is The laser beam (10) is emitted to the outside through the exit mirror (6).

FIG. 18 shows an example of the oscillation output characteristic. Here, the solid-state element (1) was made of Y _2.4 Nd _0.6 Al5O ₁₂ , and had a cross-sectional diameter of 6 mm,
Length 100mm, exit mirror (6), total internal reflection mirror (20) curvature of both 0.4mm, the distance between both mirrors 0.45m,
The reflectance of the exit mirror is 80%. The input power is the power consumed to light the flash lamp and is 3.5
A laser output of about 70 W is obtained with an input power of KW.

[Problems to be Solved by the Invention]

Since the conventional laser device uses the stable resonator as described above, the laser beam generated is a so-called higher-order mode with a large divergence angle. The index of the degree of this higher-order mode is the ratio of the cross-sectional diameter of the lowest-order mode with even phases that can occur in the resonator to the cross-sectional diameter of the laser medium. In this example, the lowest mode is a so-called Gaussian beam with a normal distribution, so the cross-sectional diameter φ0 defined at the point where its intensity is 1 / e2 of the center is the distance L between both mirrors and the wavelength λ of the laser beam. Is calculated. On the other hand, since the cross-sectional diameter of the laser medium is 6 mm, the ratio of the two is very large, about 11, and from this value it is empirically predicted that higher-order modes of the order of 100 are generated. The order of the higher-order mode is experimentally measured by measuring the divergence angle of the generated laser beam. An example of actual measurement is shown in FIG. 19, for example. From this figure, the divergence angle is understood to be about 10 mrad, and it is calculated that the order of the corresponding higher-order mode is about the 100th order. It can be said that the size of this divergence angle is the focusing performance of the laser beam itself. This is because the focusing spot diameter φs of the focusing lens with the focal length f is roughly represented by φsf · θ with respect to the divergence angle θ, and therefore the size of the focusing spot diameter is proportional to the divergence angle. Is determined. 10 here
Comparing the value of mrad with a commercially available CO ₂ laser, it is about 10
Therefore, it can be said that the condensing characteristic of the conventional solid-state laser device is 1/10 of that of the CO ₂ laser device. Further, there is a problem that the magnitude of the divergence angle largely changes depending on the applied power and hence the laser output as shown in FIG. This is because the solid state element (1) becomes a lens due to the temperature gradient generated in the solid state element (1), and the resonance state is destroyed. For this reason, it has been observed that, for example, if the input power is further increased, the oscillation becomes extremely unstable at 3 to 4 KW or more.

The present invention has been made to solve the above problems, and an object thereof is to obtain a laser device capable of stably generating a laser beam regardless of the magnitude of the laser output.

[Means for Solving the Problems]

A laser device according to the present invention includes a plurality of optical elements forming a laser resonator, a laser medium disposed between these optical elements, and any one of the above optical elements or the above laser medium, It is provided with a drive system that moves in the optical axis direction in accordance with the amount of input energy.

The laser resonator may be an unstable resonator.

In addition, as a mirror that constitutes the above unstable resonator,
It may be composed of an exit mirror and a total reflection mirror having a partial reflection part in the center and a non-reflection part around it.

Further, means for canceling the phase difference between the laser beams passing through the partial reflection portion and the non-reflection portion can be provided.

[Action]

In the laser device according to the present invention, even if the energy input to the laser medium increases and the laser medium becomes a lens, the divergence angle change of the emitted beam due to this is canceled out, and the parallel beam is always taken out stably.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, (1) is a solid-state element, for example, in the case of a YAG laser, for example, a rod-shaped crystal made of Y _3-X NdxAl5O ₁₂ , (2) is a total reflection mirror provided on the end face of this rod, 3) is a light source, for example, an arc lamp, (4) is a power source for lighting the arc lamp (3), (5) is a condensing reflection mirror, (6) is an exit mirror made of glass, (7) ) Is a partially reflective film made of, for example, TiO _{2 provided} in the center of the inner surface of the exit mirror (6), and (8) is a partially reflective film on the inner surface of the exit mirror.
On the outer periphery of (7), the outer surface of the exit mirror (6), and further the solid state element
A non-reflective film made of, for example, SiO ₂ on the end face of (1), and (9) and (11) are laser beams generated in a laser resonator consisting of an exit mirror (6) and a total reflection mirror (2). , (10) is a laser beam taken out of the laser resonator, (12) is an outer beam, and (30) is a linear stage that moves the exit mirror (6) along the laser beam emitting direction, that is, the optical axis direction. is there.

Next, the operation will be described. The solid-state element (1) is excited by direct light from the arc lamp (3) turned on by the power supply (4) and reflected light from the condensing reflection mirror (5) to form a laser medium. On the other hand, the laser beams (9), (1) generated in the laser resonator consisting of the exit mirror (6) and the total reflection mirror (2)
1) is amplified by this laser medium, and when it reaches a certain size or more, part of it is extracted as a laser beam (10) to the outside.

The laser resonator will be described in more detail. The exit mirror (6) and the total reflection mirror (2) constitute a so-called negative branch unstable resonator. Laser beam (11)
Is amplified by a solid medium, then condensed by a total reflection mirror and amplified by a solid medium to become a laser beam (9). The peripheral part of this laser beam (9) is the peripheral part of the inner surface of the exit mirror (6). Most of it is emitted to the outside by the action of the non-reflective film, and part of it is taken out to the outside by the action of the partially reflective film in the center of the inner surface of the exit mirror (6), and the remaining part is the laser beam. As (11), it reciprocates in the laser resonator again. Therefore, the external laser beam (10) has a hollow shape. Moreover, in such an unstable resonator, the difference in loss between the lowest-order mode with uniform phase and the higher-order mode is much larger than that of the stable resonator, so the laser beam generated after several round trips is the lowest-order mode. Only the ones. Also, the radius of curvature of the outer surface of the exit mirror is smaller than the radius of curvature of the inner surface, and it has a meniscus shape, and the outgoing beam is substantially parallel. After all, from these things,
The most ideal laser beam, which is a collimated parallel beam having a uniform phase, can be obtained.

FIG. 2 shows an example of the oscillation output characteristic. Here, the solid-state element (1) was made of Y _2.5 Nd _0.6 Al5O ₁₂ , and had a cross-sectional diameter of 6 mm,
The length of 150mm, the curvature of the inner surface of the exit mirror (6) and the total reflection mirror (2) are 0.48m and 0.6m respectively, and the distance between both mirrors is
The reflectance of the partial reflection film (7) at the center of the inner surface of the exit mirror (6) is 0.44 m and 80%. The input power is the power consumed to light the flash lamp, and about 3 KW of input power is about 5
A laser output of 0 W is obtained.

Figure 3 shows the pattern of the laser beam focused by the lens.
At a laser output of 100 W, a solid-state laser device according to an embodiment of the present invention (FIG. 3 (a)) and a conventional solid-state laser device (FIG. 3 (b)) are shown for comparison.
According to the present invention, not only is the width reduced to about 1/40 of that of the conventional one, but the central axial strength is 1000 times or more.

Next, the movement of the exit mirror (6) by the linear stage (30), which is the main part of the present invention, will be described in detail. As explained in the conventional example, when excited by the lamp (3), a refractive index distribution caused by the temperature distribution is generated in the solid state element, and the solid state element acts equivalently as a convex lens for the laser beam passing through it. To do. FIG. 4 shows the laser beam optical path in the steady state generated in the resonator when the equivalent convex lens is generated in the resonator. (90), (91) in the figure
Is a laser beam, (100) is a convex lens (f = 0.25 m) representing the action of the exit mirror (6), (101) is a convex lens (f = 0.3 m) representing the action of the total reflection mirror (2), (102) Is a solid element
It is an equivalent convex lens of (1). The optical path inside the lens (100) is obscured, which means that the laser beam is extracted to the outside by the non-reflection film (8) on the inner surface of the exit mirror (6). In Fig. 4 (a), the input power is 1.9 kW,
Figures (b) and (c) show the case of 3 kW. The laser beam (9) partially reflected by the partially reflecting film (7) on the inner surface of the exit mirror (6)
0) passes through the equivalent lens of the solid-state element twice, and is also focused on the lens (101) corresponding to the total reflection mirror in the meantime to become the laser beam (91), and the outer peripheral portion is taken out to the outside.
Part of the inner circumference is the lens (100) corresponding to the exit mirror (6)
By the action of, the laser beam reciprocates in the resonator as a parallel laser beam (90). In Fig. 4 (a), the applied power is small, and therefore the focal length of the equivalent lens of the solid-state element is about 1.
Since it is as large as m, the emitted laser beam (90) is kept parallel. However, when the input power shown in FIG. 4 (b) is large, the focal length of the equivalent lens of the solid-state element is about 0.5 m, which is close to the equivalent focal length of 0.3 m of the lens (101) corresponding to the total reflection mirror. Outgoing beam due to that effect (90)
It can be seen that is convergent. However, when the exit mirror (6) is driven on the linear stage in this state and the total reflection mirror is moved about 0.05 m, the outgoing beams can be kept parallel again as shown in FIG. 4 (c). Considering the conditions for keeping these parallel, the lenses (100), (101), (1
The focal lengths of 02) are f1, f2 and f3 respectively, and the lens (100),
Since the distance between (102) is small, if these are integrated and considered as one lens, the distance L between both mirrors is Is the so-called conformal condition, which is the condition that the outgoing beams are parallel. Therefore, if the applied power changes and the focal length of the solid state element is shortened by Δf3, In this case, ΔL is calculated to be 0.048 m, which is almost the same as that shown in Fig. 4.

In the above embodiment, the central portion of the inner surface of the exit mirror has a partial reflectance, but it may have a total reflectance as shown in FIG. In this case, a ring-shaped laser beam is generated, and the focusing effect deteriorates due to the diffraction effect caused by the ring shape, but a sufficiently high-quality laser beam can be generated as compared with the conventional example.

Further, in the above-mentioned embodiment, the phase difference between the laser beams passing through the central portion and the peripheral portion of the inner surface of the exit mirror is small and has no problem.However, this is a problem depending on the structure of the partial reflection film (7). In that case, a means for canceling the phase difference between the two laser beams may be provided. For example, as shown in FIG. 6, a step (7) is formed on the outer surface of the exit mirror (6).
Providing 1), the partial reflection film (7) and the non-reflection film on the inner surface of the exit mirror
An optical path difference may be provided between the laser beams passing through (8), or the laser beam may be extracted through a wind mirror (72) having a step (71) as shown in FIG.

Further, although the total reflection mirror (2) is formed on the side surface of the solid-state element in the above-mentioned embodiment, both may be separated as shown in FIG. Further, the solid-state element may be installed near the exit mirror (6) as shown in FIGS.

Further, in the above embodiment, an example in which a condensed laser beam is reflected from the total reflection mirror is shown, but a parallel laser beam may be reflected, as shown in FIGS.
11 and 12 in correspondence with FIGS. 9 and 10.
Modifications shown in FIGS. 13, 13 and 14 are possible.

Further, the mirror may be driven by moving the total reflection mirror (20) as shown in FIG.
(1) Even if the lens itself is moved as shown in FIG. 16, the same optically as in FIG. 1 can be realized.

Further, in the above embodiment, the unstable resonator has a negative branch structure and the solid-state element is arranged in the vicinity of the mirror. It may be at the center between the mirrors. However, in these cases, the movement amount of the mirror and the solid-state element becomes larger than that shown in the above-mentioned embodiment.

Further, although the solid-state laser device has been described in the above embodiment, it can be applied to any device in which the temperature distribution of the laser medium acts like a lens.

〔The invention's effect〕

As described above, according to the present invention, a drive system that moves any one of a plurality of optical elements forming a laser resonator or a laser medium in the optical axis direction in accordance with the amount of energy input to the laser medium is provided. Since it is provided, there is an effect that the lensing of the laser medium is canceled and a parallel high-quality laser beam can be stably obtained.

Further, when an unstable resonator is used as the laser resonator, there is an effect that a laser beam with a small divergence angle can be obtained.

In addition, if an exit mirror and a total reflection mirror having a partial reflection part in the center and a non-reflection part in the periphery are used as the mirrors forming the unstable resonator, a high-quality beam with good condensing property can be obtained. You can Further, in this case, by providing means for canceling the phase difference between the laser beams passing through the partially reflecting portion and the non-reflecting portion, the beam quality is further improved.

[Brief description of drawings]

FIG. 1 is a sectional configuration diagram showing a solid-state laser device according to an embodiment of the present invention, FIG. 2 is a characteristic diagram showing its output characteristics, and FIG.
FIGS. 4 (a) and 4 (b) are characteristic diagrams showing focusing patterns in one embodiment of the present invention and a conventional solid-state laser device, respectively.
(b) and (c) are explanatory views for explaining the operation of the solid-state laser device according to one embodiment of the present invention, and FIGS. 5 to 16 are cross-sectional structural views showing a laser device according to another embodiment of the present invention. ，
FIG. 17 is a sectional configuration diagram showing a conventional solid-state laser device, and FIGS. 18 and 19 are characteristic diagrams showing laser output and divergence angle in the conventional solid-state laser device, respectively. (1) ... Solid state element, (2) (20) ... Total reflection mirror, (3) ... Light source,
(6)… Exit mirror, (7)… Partial reflection film, (8)… No reflection film,
(9) (10) (11)… laser beam, (30)… linear stage,
(71)… Step. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (4)

[Claims] 1. A plurality of optical elements constituting a laser resonator,
A laser medium provided between these optical elements, and a laser provided with a drive system for moving one of the optical elements or the laser medium in the optical axis direction in accordance with the amount of energy input to the laser medium. apparatus. 2. A plurality of laser mirrors constituting an unstable laser resonator, a laser medium arranged between these mirrors,
And a laser device including a drive system for moving any of the mirrors or the laser medium in the optical axis direction in accordance with the amount of energy input to the laser medium. 3. A laser device according to claim 2, wherein the laser resonator comprises a partial reflection portion in the center and an exit mirror and a total reflection mirror each having a non-reflection portion in the periphery thereof. 4. The laser device according to claim 3, further comprising means for canceling the phase between the laser beams passing through the partially reflecting portion and the non-reflecting portion.